Snow just wasn't in the cards

Many Houma-Thibodaux residents awoke Wednesday morning to a surprise: dry pavement with little to none of the snow and ice accumulation that had been forecast.

John HarperStaff Writer

Many Houma-Thibodaux residents awoke Wednesday morning to a surprise: dry pavement with little to none of the snow and ice accumulation that had been forecast.South Louisiana would have been in for a white morning if it hadn’t been for a gasp of warm air that effectively shot down the chance of snow, according to the National Weather Service.Ken Graham, meteorologist in charge at the weather service station in Slidell, said the mix of freezing rain and sleet, along with the absence of fluffy white snow, was explained by a weather balloon he sent 120,000 feet into the atmosphere Tuesday afternoon.As the balloon rose, temperatures started getting warmer, opposite of what is normally expected by meteorologists. This temperature inversion made the formation of snow all but impossible, Graham said. “If we didn’t have that warm node in the temperature profile we would have had quite a lot of snow,” Graham said. “The profile was not one of snow but of sleet and ice.” It was a southwest wind, slightly warmer than the freezing cold west winds that spun off of the latest Arctic blast, that jammed up the storm and nixed youngsters’ hopes of building snowmen. “As a result of that, you would see some snow mixed in, but it was never a profile to get a whole lot of snow,” Graham said. As snow fell into this warm pocket of air it melted into rain, either refreezing into sleet or hitting the ground and freezing as slick ice. At the same time the cool moisture evaporated as it fell, drawing down the cold air and pulling down nighttime temperatures. As the air cooled it also dried out, Graham said, which meant that ice forming overnight evaporated in a process called sublimation. “You usually think of ice melting and then evaporating,” Graham said. “In this case when it’s dry enough it can go straight from a solid to a gas. It actually skips the liquid phase. ... That’s called sublimation.”Ice on bridges, which is super cooled by wind passing both above and below the spans, stuck around in many areas. That closed bridges and the elevated portion of La. 1, even as ice on pavement, cars and homes escaped into 15- to 20-mph winds. Graham said he expected at least some of that ice to stick around Wednesday night, when temperatures were forecast to again dip below the freezing mark before warmer air moves in today, pushing temperatures into the 50s. “Believe it or not, we’re looking at probably 70-degree temperatures by the time we get to Saturday,” Graham said. “That’s the roller coaster of Louisiana weather.”